ABSTRACT

Cassava is a starchy root crop that is among the most important tropical food crops in the world. The plant is endowed with a number of characteristics and exciting potential role in combating food shortage and ensuring food security. Cassava have varying root yield that are also environmental dependent. Field experiments were carried out in 2016/2017 and 2017/2018 planting seasons to assess twenty four (24) cassava genotypes for yield and reaction to diseases across four agro-ecological zones of Nigeria. The trial was laid out in a randomized complete block design with three replications at Umudike, Otobi, Minjibir and Aliero. The main aim of the study was to; identify high yielding cassava genotypes with good adaptation to the different agro-ecological zones, determine yield stability of the cassava genotypes in these environments, assess the responses of the cassava genotypes to major pest and diseases of cassava genotypes and determine inter-relationships of roots yield and associated traits among the cassava genotypes. Analysis of variance (ANOVA) revealed that genotypes had a highly significant effect on most of the growth, pest, diseases, and yield and associated traits. Yield stability results therefore evidently showed that genotype, location, year, genotype x location, genotype x year and location x year were significant (p<.00I, and p<O.O5) suggesting rational distribution of genotype to agro-ecological zones with different levels of adaptation. COB 5-17 genotype exhibited high performance in root yield (13.5 t/ha) while genotype CW 52A-1 had the least mean root yield (4.50t/ha). Yield and most of the yield components performed higher in 2016/2017 than in 2017/2018 season. Correlation studies and Path Coefficient Analysis showed that fresh shoot weight, number of leaves/plant and number of roots are the most important traits contributing to cassava root yield and therefore demand close attention as selection indices for improvement of cassava genotypes. Some of the genotypes had stable yield across the four environments suggesting that cassava can easily adapt to dry ecological zones. Genotype COB 5- 17 was found to be high yielding but exhibited low yield stability across the locations in the GGE biplot ranking. The study confirmed effect of genotype and genotype by environment interaction which clearly indicated Otobi location as a good test environment for cassava research and production. The biplot also showed that genotype G19, G4and G5 were the best performing genotypes while genotypes G17, G4 and G23 were the most stable genotypes across the environments and over the two seasons.